A scintillator is a member that absorbs radiation, such as α-rays, β-rays, γ-rays and X-rays, to emit fluorescent light. The combination of a scintillator and a photodiode for detecting fluorescent light can be used for detecting the radiation received. It has been used in various fields of applied science, e.g., the medical field such as tomography, the industrial field such as nondestructive inspection, the field of security such as baggage inspection, and the academic field such as high-energy physics, for example.
Patent Document No. 1 discloses a polycrystalline scintillator that has a composition represented by the general formula: (Gd1−w−x−y−zYwLuxREyCez)3+a(Al1−u−sGauScs)5−aO12 (where RE is at least one element of Pr, Dy and Er, and 0≤a≤0.15, 0.2≤w≤0.5, 0≤x≤0.5, 0<y≤0.003, 0.0003≤z≤0.0167, 0.2≤u≤0.6, 0≤s≤0.1), has an Fe content of 0.05 to 1 mass ppm with respect to the total mass including the mass of Fe, has an Si content of 0.5 to 10 mass ppm with respect to the total mass including the mass of Si, and gives an emission intensity temperature coefficient of −0.15%/° C. to +0.15%/° C. at 30° C. to 40° C. when excited by X-rays.
Patent Document No. 1 states that by replacing Gd with Y or with Y and Lu, it is possible to improve the temperature coefficient while suppressing the decrease in emission intensity.
Patent Document No. 2 discloses a solid scintillator made of a polycrystal of a garnet structure oxide represented by the general formula: (Gd1−α−β−γTbαLuβCeγ)3(Al1−xGax)aOb (where 0<α≤0.5, 0<β≤0.5, 0.0001≤γ≤0.1, 0<x<1, 4.8≤a≤5.2, 11.6≤b≤12.4).
Patent Document No. 2 states that Tb contributes to fluorescent light and that codoping of Tb nd Ce improves the emission intensity and the afterglow characteristic.
Patent Document No. 3 discloses a scintillator that is made of a light-emitting substance having a garnet structure, includes Gd, Y, Ce, Ga and Al, is represented by (Gd1−x−y−zYxAyCez)3+u(Ga1−m−nAlmDn)5−uO12: wFO, wherein A is Lu, La, Tb, Dy or a combination thereof, D is In, Sc or a combination thereof, F is a divalent ion, where 0≤x<0.2, 0<y<0.5, 0.001<z<0.05, 0<u<0.1, 0≤n<0.2, 0.3<m<0.6 and 10 ppm≤w≤300 ppm, and where y/x>1.
Patent Document No. 3 states that by setting the ratio of Tb with respect to Y to be greater than 1 and using a divalent ion other than Mg (e.g., Ca, Sr, Ba, Zn) as a dopant, it is possible to realize a high decay rate and reduce the afterglow while keeping a high emission intensity.